W. Fischer

Brookhaven National Laboratory, New York City, New York, United States

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Publications (254)554.96 Total impact

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    ABSTRACT: A new experiment is described to detect a permanent electric dipole moment of the proton with a sensitivity of $10^{-29}e\cdot$cm by using polarized "magic" momentum $0.7$~GeV/c protons in an all-electric storage ring. Systematic errors relevant to the experiment are discussed and techniques to address them are presented. The measurement is sensitive to new physics beyond the Standard Model at the scale of 3000~TeV.
    02/2015;
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    Y. Luo, W. Fischer
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    ABSTRACT: The Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory has been in operation since 2000. Over the past decade, the luminosity in the polarized proton (p-p) operations has increased by more than one order of magnitude. The maximum total beam-beam tune shift with two collisions has reached 0.018. The beam-beam interaction leads to large tune spread, emittance growth, and short beam and luminosity lifetimes. In this article, we review the beam-beam observations during the previous RHIC p-p runs. The mechanism for particle loss is presented. The intra-beam scattering (IBS) contributions to emittance and bunch length growths are calculated and compared with the measurements. Finally, we will discuss current limits in the RHIC p-p operations and their solutions.
    10/2014;
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    ABSTRACT: To compensate the large beam-beam tune spread and beam-beam resonance driving terms in the polarized proton operation in the Relativistic Heavy Ion Collider (RHIC), we will introduce a low-energy DC electron beam into each ring to collide head-on with the opposing proton beam. The device to provide the electron beam is called an electron lens. In this article, using a 6-D weak-strong-beam-beam interaction simulation model, we investigate the effects of head-on beam-beam compensation with electron lenses on the proton beam dynamics in the RHIC 250 GeV polarized proton operation. This article is abridged from the published article [1].
    10/2014;
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    ABSTRACT: In polarized proton operation in the Relativistic Heavy Ion Collider (RHIC) coherent beam-beam modes are routinely observed with beam transfer function measurements. These modes can become unstable under external excitation or in the presence of impedance. This becomes even more relevant in the presence of head-on compensation, which reduces the beam-beam tune spread and hence Landau damping. We report on experiments and simulations carried out to understand the impact of coherent modes on operation with electron lenses.
    10/2014;
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    ABSTRACT: Each 2.6-m long superconducting e-Lens magnet assembly consists of a main solenoid coil and corrector coils mounted concentric to the axis of the solenoid. Fringe field and “antifringe field” solenoid coils are also mounted coaxially at each end of the main solenoid. Due to the high magnetic field of 6 T large interactive forces are generated in the assembly between and within the various magnetic elements. The central field uniformity requirement of ±0.50% and the strict field straightness requirement of ±50 microns over 2.1 m of length provide additional challenges. The coil construction details to meet the design requirements are presented and discussed. The e-Lens coil assemblies are installed in a pressure vessel cooled to 4.5 K in a liquid helium bath. The design of the magnet adequately cools the superconducting coils and the power leads using the available cryogens supplied in the RHIC tunnel. The mechanical design of the magnet structure including thermal considerations is also presented.
    IEEE Transactions on Applied Superconductivity 06/2014; 24(3):1-4. · 1.32 Impact Factor
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    ABSTRACT: In order to partially compensate for head-on beam-beam effects from polarized proton collisions in the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL), two electron lenses (e-Lens) have been manufactured at BNL. For each e-Lens, one for each of the two RHIC rings, a low energy electron beam and the high energy proton beam will interact in a 2.5-m-long superconducting solenoid, which is also accompanied by four other smaller solenoids and 12 corrector dipoles, all of which are superconducting and provide various tuning and corrective functions during operations. The design of this multicoil assembly is a unique and complex one, and likewise, the simultaneous operation of the coils at 4.5 K is also challenging, due to high inductance and individual magnetic fields, which interact with each other. This paper reports on the results from extensive ramp and quench tests at 4.5 K, and the proper operating procedures determined from these tests.
    IEEE Transactions on Applied Superconductivity 06/2014; 24(3):1-5. · 1.32 Impact Factor
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    ABSTRACT: To compensate for the beam–beam effects from the proton–proton interactions at the two interaction points IP6 and IP8 in the Relativistic Heavy Ion Collider (RHIC), we are constructing two electron lenses (e-lenses) that we plan to install in the interaction region IR10. Before installing them, the electron gun, collector, instrumentation were tested and the electron beam properties were qualified on an electron lens test bench. We will present the test results and discuss our measurement of the electron beam current and of the electron gun perveance. We achieved a maximum current of 1 A with 5 kV energy for both the pulsed- and the DC-beam (which is a long turn-by-turn pulse beam). We measured beam transverse profiles with an yttrium aluminum garnet (YAG) screen and pinhole detector, and compared those to simulated beam profiles. Measurements of the pulsed electron beam stability were obtained by measuring the modulator voltage.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 04/2014; 743:56–67. · 1.32 Impact Factor
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    ABSTRACT: In polarized proton operation the RHIC performance is limited by the head-on beam-beam effect. To overcome this limitation two electron lenses are under commission-ing. We give an overview of head-on beam-beam compen-sation in general and the specific design for RHIC, which is based on electron lenses. The status of installation and commissioning are presented along with plans for the fu-ture.
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    ABSTRACT: Heavy ion cross sections totaling several hundred barns have been calculated previously for the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). These total cross sections are more than an order of mag-nitude larger than the geometric ion-ion cross sections, and are primarily due to Bound-Free Pair Production (BFPP) and Electro-Magnetic Dissociation (EMD). Apart from a general interest in verifying the calculations experimen-tally, an accurate prediction of the losses created in the heavy ion collisions is of practical interest for the LHC, where some collision products are lost in cryogenically cooled magnets and have the potential to quench these magnets. In the 2012 RHIC run uranium ions collided with each other at a center-of-mass energy of 192.8 GeV per nucleon-pair with nearly all beam losses due to collisions. This allows for the measurement of the total cross section and a comparison with calculations.
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    ABSTRACT: The 2013 operation of the Relativistic Heavy Ion Collider (RHIC) marks the second year of running under the RHIC II era. This year saw the implementation of several important upgrades designed to push the intensity frontier. Two new electron lenses to compensate beam-beam effects (e-lenses) have been partially installed, along with a new lattice designed for the e-lens operation. A new polarized proton source which generates about factor of 2 more intensity was commissioned as well as a host of RF upgrades ranging from a new longitudinal damper a new Landau cavity in RHIC to a new low level RF system and new beam bunching structure in AGS. We present an overview of the challenges and results from this years run.
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    ABSTRACT: In the 2013 RHIC polarized-proton run, it was found that the intensity of the RHIC bunch had reached a limit due to the head-on beam-beam interaction at intensity of 2x10 11 , as we expected from our simulations [1]. To overcome this limitation, we have planned to implement two electron lenses for beam-beam compensation. During and after the 2013 RHIC run, some e-lens systems were commissioned. The effect of the e-lens warm solenoids on the protons orbit was observed and corrected by orbit feedback. The blue electron-lens system was fully tested, except for the superconducting magnet; the electron beam was propagated from the gun to the collector, and most of the instrumentation for the blue e-lens was commissioned. The straightness of the superconducting solenoid #2 field was measured for the first time. The installation of the yellow e-lens system and two superconducting magnets are underway.
    Particle Accelerator Conference 2013 (PAC2013), Pasadena, CA; 01/2014
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    ABSTRACT: In polarized proton operation, the RHIC performance is limited by the head-on beam-beam effect. To overcome these limitations two electron lenses were installed and are under commissioning. One lens uses a newly manufactured superconducting solenoid, in the other lens the spare super-conducting solenoid of the BNL Electron Beam Ion Source (EBIS) is installed to allow for propagation of the electron beam. (This spare magnet will be replaced by the same type of superconducting magnet that is also used in the other lens during the 2013 shut-down.) We give an overview of the commissioning configuration of both lenses, and report on first results in commissioning the hardware. We also re-port on lattice modifications needed to adjust the phase ad-vance between the beam-beam interactions and the electron lenses, as well as upgrades to the RHIC instrumentation for the commissioning.
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    ABSTRACT: As the world's only high energy polarized proton collider, the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL) has been provid-ing collisions of polarized proton beams at beam energy from 100 GeV to 255 GeV for the past decade to explore the proton spin structure as well as other spin dependent measurements. With the help of two Siberian Snakes per accelerator plus outstanding beam control, beam polariza-tion is preserved up to 100 GeV. About 10% polarization loss has been observed during the acceleration between 100 GeV and 255 GeV due to several strong depolarizing resonances. Moderate polarization loss was also observed during a typical 8 hour physics store. This presentation will give an overview the achieved per-formance of RHIC, both polarization as well as luminosity. The plan for providing high energy polarized He-3 colli-sions at RHIC will also be covered.
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    ABSTRACT: To search for the critical point in the QCD phase dia-gram, RHIC needs to operate at a set of low gold beam energies between 2.5 and 20 GeV per nucleon. During run 12, first successful collider operation at the lowest energy of 2.5 GeV per nucleon was achieved. We present the chal-lenges and achieved results, and discuss possible future up-grades and improvements.
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    ABSTRACT: In the 2012 RHIC heavy ion run, we collided uraniumuranium (U-U) ions at 96.4 GeV/nucleon and copper-gold (Cu-Au) ions at 100 GeV/nucleon for the first time in RHIC. The new Electron-Beam Ion Source (EBIS) was used for the first time to provide ions for the RHIC physics program. After adding the horizontal cooling, 3-D stochastic cooling became operational in RHIC for the first time, which greatly enhanced the luminosity. With a double bunch merging technique in the Booster and AGS, the bunch intensities of Cu and Au ions in RHIC surpassed their projections. Both PHENIX and STAR detectors reached their integrated luminosity goals for both U-U and Cu-Au collisions. In this article we review the machine improvements and performances in this run.
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    ABSTRACT: Heavy ion cross sections totaling several hundred barns have been calculated previously for the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). These total cross sections are more than an order of magnitude larger than the geometric ion-ion cross sections primarily due to Bound-Free Pair Production (BFPP) and Electro-Magnetic Dissociation (EMD). Apart from a general interest in verifying the calculations experimentally, an accurate prediction of the losses created in the heavy ion collisions is of practical interest for the LHC, where some collision products are lost in cryogenically cooled magnets and have the potential to quench these magnets. In the 2012 RHIC run uranium ions collided with each other at $\sqrt{s_{NN}} = 192.8$ GeV with nearly all beam losses due to collisions. This allows for the measurement of the total cross section, which agrees with the calculated cross section within the experimental error.
    12/2013; 89(1).
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    ABSTRACT: To rectify the problems of electron clouds observed in RHIC and unacceptable ohmic heating for superconducting magnets that can limit future machine upgrades, we started developing a robotic plasma deposition technique for $in-situ$ coating of the RHIC 316LN stainless steel cold bore tubes based on staged magnetrons mounted on a mobile mole for deposition of Cu followed by amorphous carbon (a-C) coating. The Cu coating reduces wall resistivity, while a-C has low SEY that suppresses electron cloud formation. Recent RF resistivity computations indicate that 10 {\mu}m of Cu coating thickness is needed. But, Cu coatings thicker than 2 {\mu}m can have grain structures that might have lower SEY like gold black. A 15-cm Cu cathode magnetron was designed and fabricated, after which, 30 cm long samples of RHIC cold bore tubes were coated with various OFHC copper thicknesses; room temperature RF resistivity measured. Rectangular stainless steel and SS discs were Cu coated. SEY of rectangular samples were measured at room; and, SEY of a disc sample was measured at cryogenic temperatures.
    08/2013;
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    ABSTRACT: We present in this paper our research and development of accelerator fast kicker with a solid state FID pulse generator. This is the first attempt to test a high strength fast kicker with a nano-second high pulse power generator for large hadron accelerators and colliders. The FID pulse generator features a 10 ns pulse rise time (2%-98%), 30ns pulse fall time, 50 ns flat top pulse duration, 100 Hz repetition rate, and peak amplitude of 50 kV and 1.0 kA. We have successfully tested the system with long length transmission cable, RHIC injection kicker magnet, matched and mismatched resistive load. The pulse generator is ultra compact and its size is comparable to a digital oscilloscope. The existing RHIC injection kicker system has four oil filled tri-axial Blumlein generators occupying a floor space of about 1000 square feet. A set of four FID pulse generators would fit into a single rack. It has a potential space saving of 50 to 100 times. Another advantage is its ultra fast current slew rate surpassing the thyratron and traditional modulator system. The technology is impressive and results are encouraging.
    Pulsed Power Conference (PPC), 2013 19th IEEE; 06/2013
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    ABSTRACT: In this article, we will review the techniques to measure the off-momentum β-beat and the correction algorithms with the chromatic arc sextupoles in RHIC. We will focus on the measurement and correction of the off-momentum β*-beat at the interaction points. The off-momentum β* is measured with the quadrupole strength change and a high resolution phase lock loop tune meter. The results of off-momentum β* correction performed in a dedicated beam experiment in the 2012 RHIC 250 GeV polarized proton run are presented.
    05/2012;
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    ABSTRACT: To compensate the beam-beam tune spread and beam-beam resonance driving terms in the polarized proton operation in the Relativistic Heavy Ion Collider (RHIC), we will introduce a low energy DC electron beam into each ring to collide head-on with the opposing proton beam. The device to provide the electron beam is called an electron lens. In this article, using a 6D weak-strong beam-beam interaction simulation model, we will investigate the effects of head-on beam-beam compensation with electron lenses on the proton beam dynamics for the RHIC 250 GeV polarized proton operation. Frequency maps, dynamic apertures, and proton beam loss rates are calculated for this study. Key beam parameters involved in this scheme are varied to search for the optimum compensation condition. The sensitivities of head-on beam-beam compensation to beam imperfections and beam offsets are also studied.
    Review of Modern Physics 05/2012; · 42.86 Impact Factor

Publication Stats

532 Citations
554.96 Total Impact Points

Institutions

  • 1997–2014
    • Brookhaven National Laboratory
      • • Collider-Accelerator Department
      • • Superconducting Magnet Division
      New York City, New York, United States
  • 2005
    • Cells Alba
      Barcino, Catalonia, Spain
  • 2003
    • Lawrence Berkeley National Laboratory
      Berkeley, California, United States
    • RIKEN
      Вако, Saitama, Japan
  • 2001
    • Gracie Square Hospital, New York, NY
      New York City, New York, United States